1940

Philadelphia's Franklin Institute issued a press release declaring that the world would end the following day. The release was then picked up by radio station KYW whose announcers told their listeners,

Your worst fears that the world will end are confirmed by astronomers of the Franklin Institute... Scientists predict that the world will end at 3 P.M. Eastern Standard Time tomorrow. This is no April Fool joke.

The public reaction was immediate. Local authorities were flooded with frantic phone calls. The panic only subsided after the Franklin Institute repeatedly assured everyone that it had made no such prediction. The prankster responsible for the press release turned out to be William Castellini, the Institute's press agent. He had intended to use the fake release to publicize an April 1st lecture at the institute titled How Will the World End? Soon afterwards, the Institute dismissed Castellini.